In a process of forming a multilayer wiring structure of a semiconductor device, there may be performed a plasma etching process for forming a recess in a damascene structure having a hole or a via hole on various kinds of films formed on a semiconductor wafer (hereinafter, simply referred to as a “wafer”) made of, e.g., silicon (Si).
An apparatus for performing the plasma etching process includes a mounting table for mounting thereon the wafer and a focus ring disposed to surround the periphery of the wafer mounted on the mounting table. The focus ring is provided to increase uniformity in a plasma distribution on a surface of the wafer. In order to achieve such high uniformity in the plasma distribution, it has been deemed to be effective that electrical characteristics such as an electric conductivity of the focus ring are made to be close to those of the wafer. For this reason, the focus ring may be made of Si, the same material as that of the wafer.
However, an etching target film exposed on the surface of the wafer may be made of various kinds of materials. If the material of the etching target film is different from the material of the focus ring, distribution of active species included in the plasma becomes non-uniform at the vicinity of a boundary between the wafer and the focus ring in comparison to the distribution of active species at a diametrically inner region of the wafer due to different reactions of the active species in the plasma depending on the materials. The present inventor has found out that as a result of this non-uniform distribution of the active species, an etching rate at an edge portion of the wafer becomes larger or smaller than an etching rate at a central portion of the wafer.
Each of Japanese Patent Application Publication No. 2006-140423 and Japanese Patent Application Publication No. 2008-78208 discloses a plasma etching apparatus having a focus ring. However, neither of them discloses the solution to solve the aforementioned problem.